The present embodiments relate to calibrating a positron emission tomography scanner.
Positron emission tomography (PET) is an imaging method (process) that is used in nuclear medicine and radiation therapy. During PET, a positron is emitted in a body due to radioactive decay. After a short distance, the positron enters into interaction with an electron. The interaction destroys both particles. The destruction creates a pair of gamma quanta. The quanta are at an angle of 180° from one another. The gamma quanta penetrate the body to be examined and after exiting it are recorded by two opposed detectors. A positron emission tomography scanner for imaging includes a plurality of gamma radiation detectors, which surround the patient to be examined. DE 32 08 178 A1 discloses the plurality of gamma radiation detectors being disposed in a ring.
The relevant radioactive decay may be induced, for example, by injection or inhalation of a radioactively marked radiopharmaceutical, such as a tracer. Disease information may be determined based on the spatial distribution of the tracer.
Radioactive decay involving the formation of positrons occurs during radiation therapy from the irradiation of a body, for example, as a function of the radiation dose applied. PET systems may perform such dosage validation or monitoring of the radiation therapy and particle therapy. In particle therapy, measurements are performed in order to check whether the planned radiation dose matches the dose actually applied and/or whether the spatial distribution of an applied dose matches a desired spatial distribution.
PET systems may be used with a particle therapy system and may deviate from the conventional ring form. For example, an in-beam PET system may include only two opposed detectors. The additional opening between the two detectors, for example, may be used to position the patient, or irradiate the patient with a beam passing through this opening without the beam striking the detectors.
To enable precise dosage validation, PET systems are calibrated at certain time intervals, for example, daily. Radioactive sources may be used for calibration. The radioactive sources are disposed in a treatment chamber in which the PET system is also located. The radioactive sources generate a defined activity, which is measured by the PET system. The measurements are used to calibrate the PET system. This process may, for example, include checking an existing calibration of the PET system.
Calibration is complicated, since dedicated radioactive sources have to be set up in the treatment chamber and then removed. This process requires manual intervention, involves cost, and can suffer from errors.